UNIVERSITY  OF  CALIf ORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY.  CALIFORNIA 


CHEESE  PESTS  AND  THEIR  CONTROL 


BY 

E.  R.  DEONG  and  C.  L.  ROADHOUSE 


BULLETIN  No.  343 

May,  1922 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY,  CALIFORNIA 

1922 


David  P.  Barrows,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

E.  J.  Wickson,  Horticulture   (Emeritus). 
,  Director  of  Resident  Instruction. 

C.  M.  Haring,  Veterinary  Science;  Director  of  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

H.  J.  Webber,  Citriculture;  Director  of  Citrus  Experiment  Station. 

C.  B.  Hutchison,  Plant  Breeding;  Director  of  the  Branch  of  Agriculture. 
Hubert  E.  Van  Norman,  Dairy  Management. 

William  A.  Setchell,  Botany. 
Myer  A.  Jaffa,  Nutrition. 
Ralph  E,  Smith,  Plant  Pathology. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 

John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
James  T.  Barrett,  Plant  Pathology. 
Walter  Mulford,  Forestry. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
J.  C.  Whitten,  Pomology. 
*Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 

F.  L.  Griffin,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  R.  Hoagland,  Plant  Nutrition. 

G.  H.  Hart,  Veterinary  Science. 
L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Vooriiies,  Assistant  to  the  Dean. 

DIVISION    OF    ENTOMOLOGY    AND    PARASITOLOGY 

W.  B.  Herms  S.  B.  Freebokn 

C.  W.  Woodwortii  H.  H.  Severin 

E.  C.  Van  Dyke  E.  R.  deOng 

E.  O.  Essig  G.  A.  Coleman 

division  of  dairy  industry 
C.  L.  Roadhouse  G.  D.  Turnbow 

C.  A.  Phillips 


*  In  cooperation  with  office  of  Public  Roads  and  Rural   Engineering,   U.   S.  Department  of 
Agriculture. 


CHEESE  PESTS  AND  THEIR  CONTROL 

By  E.  R.  de  ONG  and  C.  L.  EOADHOUSE 


CONTENTS 

The  economic  importance  of  cheese  pests 399 

Cheese  favorable  to  parasitic  growth 400 

Cheese  skippers  and  mites 401 

Cheese  skippers 401 

Life  history  of  the  cheese  fly 401 

Cheese  mites 404 

Life  history 404 

Feeding  habits 405 

Distribution 406 

Prevention  and  control 406 

Temperature  and  humidity 406 

Cold  storage  of  cheese 406 

Paraffining 407 

Screening 407 

Sanitation 407 

Sales  rooms  or  warm  storage  rooms 408 

Fumigation 4C8 

Preparing  for  fumigation 408 

General  directions  for  fumigation 410 

(I)  Hydrocyanic  acid  gas 412 

Materials  used  in  fumigation :...  414 

Process  of  fumigation 415 

(II)  Carbon  disulfid 416 

Process  of  fumigation 416 

(III)  Sulphur 417 

Final  control  measures 417 

Experimental  fumigation  data 418 

Possibility  of  the  absorption  of  fumigating  gases  by  cheese 419 

Effect  of  fumigated  cheese  on  mice 420 

Summary 423 

THE  ECONOMIC  IMPORTANCE  OF  CHEESE  PESTS 

Correspondence  with  cheese  dealers  and  experts  in  California, 
Indiana,  Massachusetts,  New  York,  Oregon,  Pennsylvania,  and  Wis- 
consin has  indicated  the  presence  of  cheese  mites  and  skippers  in  these 
states.  Other  sections  of  the  United  States  are  also  affected,  but  the 
states  mentioned  manufacture  the  greater  part  of  the  cheese  made  in 
this  country.  Infestation  of  cheese-curing  rooms  in  California  has  not 
been  frequent,  but  when  occurring,  has  been  persistent. 


400  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

The  cheese  manufactured  in  California  in  1920  was  valued  at 
$4,060, 104,4  while  the  total  cheese  output  for  the  same  year  in  the 
United  States  was  valued  at  $122,403,216.10  It  is  difficult  to  estimate 
the  exact  damage  due  to  cheese  pests.  The  losses  include  the  actual 
injury  due  to  the  presence  of  cheese  skippers  in  the  body  of  the  cheese, 
the  impaired  appearance  of  all  cheese  attacked  by  mites  and  skippers, 
the  annoyance  to  manufacturers  and  dealers,  and  the  expense  con- 
nected with  the  treatment  of  cheese  for  the  control  of  these  pests. 
The  presence  of  cheese  skippers  causes  an  additional  loss  to  the 
industry  through  the  sale  of  cheese  containing  the  "cheese  maggot,'' 
which  tends  to  disgust  the  purchaser  and  lessen  the  consumption  of 
cheese. 

Occurrence. — The  cheese  mite  is  likely  to  become  established  in 
dairy  sections  where  cheese  is  manufactured  in  several  plants.  It 
appears  on  aged  cheese  kept  in  curing  rooms  that  are  not  well  refrig- 
erated. Sammis  reports  that  the  cheese  mite  seems  to  appear  in  Wis- 
consin whenever  cheese  is  kept  several  months  in  an  ordinary  curing 
room.  A  large  cheese  dealer  in  New  York  states  that  nearly  every 
year  some  difficulty  is  experienced  with  cheese  mites  and  skippers.  In 
California  both  mites  and  skippers  have  been  observed  in  the  same 
curing  room.  The  mites  attack  the  surface  of  the  cheese  and  some- 
times cause  it  to  dry  and  crack,  thus  opening  the  cheese  for  the 
entrance  of  the  skipper. 

In  the  large  cheese  markets,  both  American  Cheddar  and  Swiss 
cheese  have  been  attacked.  The  Swiss  cheese,  on  account  of  its  larger 
size,  is  more  subject  to  cracking  on  the  surface  and  the  consequent 
invasion  of  the  cheese  skipper.  Soft  varieties  of  cheese,  such  as  Brick 
and  Limburger,  are  especially  subject  to  attack  from  cheese  pests 
during  the  higher  temperatures  of  the  summer  months,  since  the  sur- 
face of  these  types  is  unparaffined  and  hence  offers  less  resistance  to 
their  entrance. 

Cheese  favorable  to  parasitic  growth. — Cheese  pests  require  food, 
moisture,  and  warmth  for  their  development.  Since  cheese  is  a  con- 
centrated food,  sluggish  parasites,  such  as  cheese  mites,  can  exist  upon 
it  without  difficulty.  The  moisture  content  of  cheese  is  also  favorable 
to  parasitic  growth;  that  of  hard  cheese,  such  as  Cheddar,  averaging 
about  38  per  cent,  and  of  the  soft  varieties,  such  as  Limburger,  vary- 
ing from  38  to  44  per  cent.  The  temperature  and  humidity  of  the 
cheese-curing  room  may  and  frequently  do  favor  the  development  of 
pests;  but  since  these  factors  are  subject  to  considerable  adjustment, 
they  may  become  very  effective  agents  against  both  skippers  and  mites. 


Bulletin  343]  cheese  pests  and  their  control  401 

Both  preventive  and  repressive  measures  are,  however,  dependant  to 
a  certain  extent  upon  a  knowledge  of  the  life  history  and  habits  of  the 
different  pests,  hence  these  points  will  be  discussed  before  taking  up 
the  various  phases  of  control  work. 

CHEESE    SKIPPERS    AND    MITES 

In  almost  every  part  of  the  world  cheese  skippers*  and  mites,f  and 
at  rare  intervals  a  certain  beetle, J  are  found  feeding  on  cheese.  Refer- 
ences to  the  cheese  mite  date  back  hundreds  of  years,  the  species  found 
in  Europe  being  either  identical  with  or  closely  related  to  those 
common  in  America  and  Australia.  These  pests  are  not  confined  to 
cheese  as  a  food,  the  cheese  skipper  having  achieved  much  of  its 
notoriety  as  a  feeder  on  the  fatty  portions  of  ham  and  bacon,7  while 
the  mites  freely  attack  a  great  variety  of  other  foods.3 

CHEESE  SKIPPEES 

The  skipper  or  maggot  found  in  overripe  and  often  in  moldy  cheese 
hatches  from  an  egg  deposited  by  a  fly  (see  fig.  ] )  and  then  burrows 
into  the  cheese,  where  it  remains  until  full  grown,  when  it  comes  to  the 
surface  and  pupates.  Cheese  which  has  been  severely  attacked  shows 
slightly  sunken  areas  which,  if  cut  into,  will  be  found  soft  and  waxy. 
When  broken,  such  cheese  has  a  stringy  appearance,  the  grain  being 
entirely  lost.  This  condition  may  extend  throughout  the  interior.  To 
prevent  and  control  loss  of  this  nature,  a  knowledge  of  the  different 
stages  of  the  life  history  of  the  fly  is  essential.  The  length  of  time 
spent  in  the  various  life-history  stages  varies  with  the  temperature, 
becoming  very  irregular  in  a  temperature  kept  between  50°  arid  60°  F. 

Life  History  of  the  Cheese  Fly 

Egg. — White,  very  slightly  curved  and  narrow,  somewhat  tapering 
at  each  end.  Length,  one-thirtieth  of  an  inch  (0.7-0.9  mm.).  Usually 
deposited  singly  over  the  surface  of  the  cheese,  particularly  in  cracks 
or  broken  surfaces.  Time  required  for  hatching,  thirty  to  forty-eight 
hours  at  a  temperature  of  65°  F.,  or  one  and  one  fourth  to  four  days 
at  50°  to  70°  F. ;  at  50°  F.  and  below,  eggs  have  been  held  for  weeks, 
but  they  hatched  within  a  few  hours  when  placed  in  a  warm  room. 

*  Piophilia  casei  Linn.,  Family  Ephydridae. 

f  Tyroglyphus  siro  Gerv.,  T.  Untneri  Osb.,  T.  farinae  De  Geer,  T.  longior  Gerv., 
T.  terminalis  Banks,  Carpoglyphus  anonymous  Haller.  Family  Tyroglyphidae. 
Experimental  work  reported  herein  has  been  upon  the  first  two  species. 

t  Necrobia  rufipes  De  Geer,  Family  Cleridae.  (Commonly  known  as  the  ham 
beetle.) 


402 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 


Larva  (skipper). — The  newly  hatched  maggot  is  transparent  and 
so  small  as  to  be  barely  visible.  "When  mature,  it  is  yellowish  white 
or  light  gray,  abont  five-eighths  of  an  inch  (8  to  10  mm.)  long.  The 
head  end  of  the  larva  is  sharply  pointed  while  the  posterior  end  is 
blunt.  At  a  temperature  of  65°  to  95°  F.,  the  length  of  the  larval 
stage  is  from  eight  to  fifteen  days.  At  the  normal  temperature  (50° 
to  65°  F.)  of  most  curing  rooms,  the  larval  period  will  extend  much 
beyond  this  time  and  may  possibly  continue  for  months  at  the  lower 
temperature. 

The  peculiar  habit  of  the  larva  in  curving  the  ends  of  the  body 
together  and  then  suddenly  springing  to  a  distance  of  from  three  to 
six  inches  has  given  it  the  name  of  "skipper." 


)    v 


Fig.  1. — Illustrating  the  life  history  of  the  cheese  fly;  left  to  right, 
egg,  larva   (skipper),  pupa,  adult  fly.      (X  4.) 


Pupa. — The  larva  when  mature  seeks  a  secluded  place  and  there 
changes  into  a  pupa,  a  hard-shelled,  brown  case,  about  one-fifth  of  an 
inch  (4  to  6  mm.)  long.  These  pupae  will  be  found  scattered  about 
under  the  cheesecloth  covering  or  in  dark  places  on  the  shelves.  Length 
of  pupal  stage,  sev<  n  to  twelve  days  at  65°  to  95°  F.,  twelve  to  fourteen 
days  at  55°  to  60°  F. ;  at  50°  F.  and  below,  pupae  were  held  for  five 
weeks  without  any  flies  appearing,  but  within  ten  hours  after  removal 
to  a  temperature  of  80°  P.,  90  per  cent  of  the  flies  had  emerged  from 
the  pupae.  Pupae  held  at  80°  to  90°  F.  showed  a  10  per  cent 
emergence  on  the  tenth  day,  an  additional  40  per  cent  on  the  eleventh, 
and  the  remainder  on  the  twelfth  day. 

Adult.-  A  dark,  bronze  fly  with  wings  overlapping  almost  to  the 
tip  when  a1  rest,  about  one-third  the  size  of  the  common  house  fly  (see 
fig.  2).  Average  length  of  life  in  confinement  is  seven  to  twenty  days. 
Copulation  occurs  within  two  or  three  days  after  emergence  from  the 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR   CONTROL 


403 


pupa  at  a  temperature  of  65°  to  95°  P.  Oviposition  begins  two  to 
four  days  later,  making  a  total  of  from  four  to  seven  days  after 
emerging  from  the  pupa  before  the  eggs  are  deposited. 

Habits. — The  cheese  fly  frequents  storage  and  curing  rooms  and 
other  situations  where  suitable  breeding  places  may  be  found.  They 
seem  to  prefer  darkness  rather  than  light,  although  they  may  go  to  a 
window  in  an  effort  to  escape  from  uncongenial  surroundings.  Eggs 
have  been  deposited  upon,  and  the  skipper  reared  from,  bacon,  ham, 
slightly  putrid  beef,0  and  oleomargarine,  as  well  as  cheese.  The  food 
usually  preferred,  however,  is  cheese.  Cheese  skippers  have  been  found 
in  butter  packing  rooms,  but  apparently  they  were  feeding  on  other 
substances  besides  the  butter  fat,  since  larvae  confined  on  butter  alone 


Fig.  2. — Showing  comparative  size  and  general  appearance  of  the  house-fly 
(left)  and  the  cheese  fly  (right).  The  latter  lays  the  eggs  from  which  the 
skipper  hatches.     (X  4.) 


did  not  come  to  maturity.  The  presence  of  the  skippers,  in  such  a 
situation,  however,  emphasizes  the  need  of  sanitation  throughout  the 
factory.  It  also  shows  the  danger  in  the  escape  of  the  cheese  flies  from 
infested  rooms  in  the  factory. 

Fresh  cheese,  even  when  unparaffined,  seems  to  be  without  attrac- 
tion to  the  fly.  In  one  infested  factory,  no  eggs  were  found  on  cheese 
less  than  three  weeks  old,  although  flies  were  abundant  in  the  curing 
room  at  the  time.  Cheese  one  month  old  was  occasionally  attacked,  but 
in  most  instances  that  three  months  old  or  more  was  preferred.  On 
paraffined  cheese,  eggs  were  found  only  where  the  coating  was  broken 
and  then  only  on  the  exposed  or  immediately  adjoining  surface. 

The  larval  habit  of  coming  to  the  surface  to  pupate  is  of  significance 
in  fumigation  work,  as  will  be  shown  later,  because  the  pupa  has  been 
found  more  or  less  susceptible  to  fumigation  with  hydrocyanic  acid 
gas,  while  the  skipper  is  practical!}'  safe  when  buried  in  the  cheese. 


404 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


CHEESE  MITES 

A  brown  powder  scattered  over  the  surface  or  in  small  depressions 
of  the  cheese  is  an  indication  of  the  presence  of  mites.  In  prolonged 
attacks,  this  powder  may  accumulate  to  the  depth  of  one-half  inch  or 
more  and  fill  cavities  extending  throughout  the  cheese.  This  powder 
consists  of  the  dead  bodies  of  mites,  molted  skins,  excreta,  tiny  particles 
of  uneaten  cheese,  and  living  mites.  The  mites  are  pale,  soft-bodied 
animals  just  visible  as  small  white  specks.  The  body  is  usually  twice 
as  long  as  broad,  with  several  conspicuous,  long  spines  (fig.  4).  In 
the  adult  and  nymphal  stages  the  mite  is  eight-legged,  but  in  the 
youngest  stage  it  has  but  six  legs. 


Fig.  3.  Cheese-fly  wing,  upper  figure.     House-fly  wing,  lower  figure.     (X  4.) 


Life  history. — Data  concerning  the  different  stages  and  develop- 
ment of  a  typical  cheese  mite  have  been  gathered  by  Nellie  B.  Eales,2 
from  whose  description  the  following  extract  is  made : 

The  life  history,  which  is  similar  in  all  the  species,  consists  of  four  stages, 
the  egg,  larva,  nymph  and  adult  male  or  female.  From  egg  to  adult  stage 
occupies  about  four  or  five  weeks.  In  working  out  the  life  history  the  method 
suggested  by  Michael  was  used.s  The  eggs  were  white,  oval  bodies,  so  small  as 
to  be  only  just  visible  to  the  naked  eye.  They  hatch  in  about  ten  to  twelve 
days  after  being  laid.  On  hatching  the  young  mite  is  known  as  a  larva.  It  is 
colorless  and  of  glassy  appearance,  and  has  three  pairs  of  legs  only.  The  larva 
feeds  actively  for  about  a  week,  then  becomes  quiescent  and  casts  its  skin, 
emerging  as  the  first  nymph.  The  first  nymph  has  four  pairs  of  legs  and 
is  somewhat  larger  than  the  larva.  It  moults  again  and  becomes  the  second 
nymph,  larger  and  more  highly  chitinised  than  the  first  nymph.  After  its  third 
moult,  the  nymph  emerges  as  an  adult  male  or  female,  the  sexual  organs  not 
being  functional  until  the  final  stage  is  reached. 

In  Tyroglyphus  longior,  however,  there  is  an  additional  stage  after  the  first 
nymph  stage,  which  is  specially  adapted  for  distributing  the  species.  This  is 
known  as  the  Jlypopus  stage  and  occurs  under  favorable  conditions,  when  the 
mites  are  allowed  to  breed  unchecked.  The  hypopus  is  like  a  minute  tortoise. 
It  is  extremely  small,  pinkish  in  color,  and   h:is  a  hard,  shelly  back  of  chitin. 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR  CONTROL 


405 


The  legs  are  short,  the  mouth  parts  rudimentary,  and  there  is  no  evidence  that 
it  feeds.  On  its  ventral  side  it  has  a  sucker  plate  by  means  of  which  it  attaches 
itself  to  other  mites,  flies,  and  moths  which  alight  on  the  cheese,  or  even  to 
the  skin  and  clothes  of  human  beings.  Tt  is  thus  carried  about  until  it  finds  a 
suitable  place,  when  it  drops  off,  moults  to  become  a  second  stage  nymph,  and 
commences  feeding. 

Michael5  states:  "hypopi  development  is  most  free  under  normal 
conditions,  ...  it  apparently  being  a  natural  stage  in  the  develop- 
ment, although  all  individuals  did  not  pass  through  this  state." 


Fig.  4. — Enlarged  drawings  of  the  cheese  mites  Tyroglyphus  farinae   (left) 
and  T.  lintneri  (right)    (after  Banks). 


Feeding  habits. — Mites  attack  cheese  in  various  degrees  of  ripeness, 
but  prefer  the  older  stocks,  providing  these  have  not  dried  out.  Like 
the  cheese  skipper,  they  are  usually  found  at  breaks  in  the  coating  of 
paraffin,  in  sheltered  places,  such  as  the  cloth  cover,  or  underneath 
the  cheese.  Mites  obtain  water  only  as  it  is  present  in  their  food; 
hence,  if  cheese  becomes  very  dry,  they  cannot  subsist  upon  it.  Feed- 
ing is  effected  by  means  of  pincher-like  mandibles  with  which  particles 
of  food  may  be  broken  off  and  chewed.  The  mites  which  attack  cheese 
vary  in  their  feeding  habits,  and  may  feed  on  starchy  materials,  such 


406  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

as  grain  and  its  by-products,  sugar,  and  dried  fruits.  They  are 
common  visitors  in  grocery  stores  and  wherever  foods  are  stored  for 
any  length  of  time. 

Distribution. — Mites  may  crawl  from  cheese  to  cheese,  especially  if 
the  room  is  dark.  Since  such  movement,  however,  is  necessarily 
limited,  dispersal  depends  principally  on  indirect  methods.  They  may 
attach  themselves,  in  the  hypopus  state,  to  moving  objects  or  may  be 
carried  on  the  clothing  of  those  working  in  the  cheese  rooms,  or  on 
equipment,  and  thus  unwittingly  be  distributed.  Mites  in  the  younger 
stages  may  also  be  carried  by  sudden  drafts  of  air. 

PREVENTION    AND   CONTROL 

The  cheese  skipper  and  the  cheese  mite,  although  differing  in  their 
life  histories,  thrive  and  develop  in  a  similar  environment.  Dirty 
storage  rooms,  greasy  shelves,  old  but  moist  cheese  with  broken  paraffin 
coating  in  close  proximity  to  the  curing  stocks,  slightly  humid  atmo- 
sphere, and  a  temperature  of  55°  to  ^0°  F.  all  favor  the  development 
of  these  pests,  once  they  become  established.  If  these  conditions  are 
guarded  against,  the  more  drastic  measures  of  fumigation  should 
seldom  if  ever  be  required. 

Temperature  and  humidity. — -Both  skippers  and  mites  are  checked 
in  their  development  by  temperatures  of  30°  to  36°  F.  Prolonged 
exposure  at  this  degree  of  cold  may  kill  the  cheese  fly  in  any  stage, 
unless  it  be  the  egg,7  but  mites  are  more  resistant  to  low  temperature. 
According  to  experiments  on  one  species,  five  months  exposure  to 
temperatures  of  10°,  25°,  30°,  and  36°  F.  killed  only  60  to  80  per  cent. 
Heat  is  much  more  dangerous  to  the  mite  than  cold.  Eales2'J  reports 
that  a  temperature  of  05°  F.  in  a  dry  atmosphere  was  fatal  to  the 
mites  but  the  same  degree  of  heat  in  a  humid  atmosphere  was  harmless, 
and  suggests  that  dipping  cheese  in  hot  water  is  not  a  good  practice. 
Whitemarsh11  found  that  the  mites  infesting  cereals  were  killed  when 
exposed  to  a  temperature  of  135°  F. 

('old,  storage  of  cheese. — kSIow  curing  of  cheese  at  temperatures  of 
30°  to  36°  F.  prevents  loss  through  cither  skippers  or  mites.  Even  up 
to  50°  F.  injury  from  these  pests  is  greatly  restricted,  but  above  this 
temperature  activity  and  reproduction  increase  rapidly.  A  commend- 
able practice,  frequently  followed  in  large  cheese-producing  regions, 
is  to  place  llio  cheese  in  curing  rooms  at  a  temperature  of  50°  to  60°  F. 
for  one  or  two  weeks  only,  followed  by  storage  at  30°  F. 

Cheese  is  held  in  the  curing  room  from  one  to  four  months,  depend- 
ing upon  the  market  demand,  if  cold  storage  is  not  available,  or  if  the 
cheese  is  marketed  direel  to  IIh*  retailer.     Under  such  conditions,  the 


Bulletin  343]  cheese  pests  and  their  control  407 

danger  of  infestation  is  greatly  "increased,  particularly  in  the  summer. 
Certain  markets  will  consume  cheese  held  for  a  shorter  period,  and 
it  may  be  considered  good  factory  management  where  cheese  pests  are 
troublesome  to  market  the  cheese  when  one  or  two  weeks  old  or  to  place 
it  in  cold  storage  until  ready  for  consumption. 

Paraffining. — Fresh  cheese  is  apparently  unattractive  to  the  cheese 
fly  and  the  mite,  hence  there  is  little  danger  of  attack  during  the  first 
few  days  of  the  curing  period,  but  as  ripening  progresses  the  danger 
increases.  As  a  protection  against  infestation,  and  for  other  reasons, 
it  is  customary  to  dip  the  cheese,  when  four  to  six  days  old,  in  paraffin 
heated  to  at  least  220°  F.  This  treatment  covers  the  cheese  with  a  thin 
coating  of  wax,  which  prevents  shrinkage  in  weight  through  loss  of 
moisture;  preserves  the  palatability  of  the  cheese,  and  aids  materially 
in  protecting  it  from  pests.  However,  the  cheese  must  be  turned  on 
the  shelves  during  the  curing  period,  the  paraffin  coating  is  frequently 
broken  and  its  protective  value  thereby  reduced.  If  cheese  is  held 
unnecessarily  long  in  the  bath,  the  butter  fat  will  melt  at  the  surface 
of  the  cheese  and  mix  with  the  melted  paraffin  in  gradually  increasing 
quantities.  Such  a  mixture  weakens  the  coating,  thus  greatly  lessen- 
ing its  protective  value,  and  may  even  serve  as  food  for  the  pests. 
Experiments  with  half-grown  skippers  confined  with  perfectly  paraf- 
fined cheese  resulted  in  their  death,  while  larvae  of  the  same  age,  con- 
fined with  unparaffined  cheese  came  to  maturity.  Paraffining  should 
be  considered  as  a  protective  measure  against  infestation  rather  than 
as  a  cure,  and  for  this  reason  every  effort  should  be  made  to  keep  the 
coating  intact,  so  that  neither  skippers  nor  mites  will  find  a  point  of 
entrance. 

Screening. — It  is  desirable  to  screen  cheese-curing  rooms,  and  even 
the  entire  factory,  particularly  when  located  near  other  factories  or 
cheese  handling  rooms,  in  order  to  prevent  the  entrance  of  the  cheese 
fly.  For  such  protection,  wire  screen  cloth,  24  meshes  to  the  inch,  should 
be  used.  Common  window  screening  having  only  14  to  16  meshes  to 
the  inch  will  not  exclude  the  fly  unless  cheese  cloth  is  tacked  over  its 
surface. 

Sanitation. — Thorough  cleanliness  in  the  cheese  factory,  and 
especially  in  the  curing  room,  is  the  best  safeguard  against  both  mites 
and  skippers.  Accumulated  grease  on  the  shelves  should  be  removed 
and  no  old  cheese  or  scraps  should  be  allowed  to  collect  in  or  near  the 
building.  Any  such  material  should  be  disposed  of  promptly  by  burn- 
ing or  utilized  as  a  food  for  stock.  If  not  removed  it  may  serve  as  a 
breeding  place  for  the  cheese  fly  and  mite,  which  upon  maturity  may 
find  their  way  into  the  curing  room.    Avoid  bringing  into  the  factory 


408  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

any  cheese  from  public  warehouses  or  other  factories;  or  using  old 
cheese  containers,  unless  it  is  known  positively  that  there  is  no  clanger 
of  introducing  pests  by  their  use.  Cheese  presses  and  all  apparatus 
where  particles  of  cheese  or  other  food  might  accumulate  should  be 
frequently  and  thoroughly  sterilized  with  boiling  water  or  steam. 

Sales  rooms  or  warm  storage  rooms. — The  public  sales  room  may 
frequently  receive  and  store  infested  cheese.  Here  sanitation  is  like- 
wise necessary  to  prevent  infestation  of  clean  stocks.  Precautions 
should  be  taken  against  storing  infested  stocks  in  the  same  room  with 
uninfested  cheese.  The  cheese  fly  moves  about  readily  and  is  quickly 
attracted  to  suitable  food.  The  mite  is  more  restricted  in  its  move- 
ments, but  on  account  of  its  small  size  it  is  easily  overlooked  and  may 
remain  inactive  in  the  dormant  condition  for  weeks  and  then  suddenly 

begin  an  attack. 

FUMIGATION 

Exposing  the  cheese-curing  room  or  factory  to  a  poisonous  gas  is 
the  most  efficient  method  known  for  controlling  both  skippers  and 
mites.  For  such  work,  the  gas  from  sodium  cyanid  (hydrocyanic  acid 
gas),  carbon  disulfid,  or  even  burning  sulfur  may  be  used,  their 
efficiency  being  in  the  order  named.  All  three  of  these  materials  have 
been  suggested  by  writers  as  possible  fumigants,  although  with  doubt 
as  to  their  value.8  Hydrocyanic  acid  gas  has  proved  the  most  effective, 
particularly  against  the  pupal  stage  of  the  fly,  in  the  work  reported 
herein.  It  is,  however,  more  dangerous  to  the  operator  than  carbon 
disulfid,  although  the  latter  is  very  explosive.  Both  materials  should 
be  used  with  great  caution.  The  use  of  burning  sulfur  is  safest,  but 
since  it  is  less  effective  against  the  skipper,  it  cannot  be  generally 
recommended  for  this  purpose,  unless  it  be  for  the  adult  fly  alone. 
Whatever  material  is  used,  prompt,  thorough  work  is  essential ;  other- 
wise the  infestation  may  spread  to  such  an  extent  as  to  make  it  difficult 
to  exterminate  the  pests. 

Preparing  for  fumigation. — The  room  to  be  fumigated  should  have 
a  tightly  constructed  floor  of  matched  lumber  or  a  concrete  floor.  All 
cracks,  ventilator  openings,  knot  holes,  and  loosely  fitting  window 
sashes  should  be  closed  with  some  wet  substance  or  should  have  paper 
pasted  over  them.  Wet  strips  of  newspaper  will  usually  stay  in 
position  for  a  sufficient  length  of  time.  The  use  of  a  thin  flour  paste 
with  a  heavy  sized  paper  will  answer  all  purposes,  and  it  is  much 
easier  to  remove;  the  paper  so  fastened  than  that  attached  with  glue 
or  gummed  strips.  The  fumigation  must  be  done  thoroughly,  for 
unless  a  large  amount  of  gas  can  be  held  in  the  room  for  a  number  of 
hours,  the  operation  will  probably  be  a  failure. 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR   CONTROL 


409 


Curing  rooms,  used  at  normal  temperature  (50°  to  60°  F.)  should 
be  built  so  that  successful  fumigation  is  a  possibility  without  the 
necessity  of  temporarily  tightening  the  room.  Such  construction  need 
not  necessarily  differ  very  much  from  that  in  common  use.  Infestation 
of  curing  or  storage  rooms,  especially  by  the  cheese  mite,  is  not  unusual, 


Fig.  5. — Junior  cheese  with  section  removed,  showing  larva   (skipper) 

at  the  point  of  entrance. 

and  eradication  is  much  easier  in  properly  constructed  rooms  than 
where  cracks  or  openings  occur.  The  type  of  construction  should  be 
uniform  throughout,  with  walls  and  ceilings  made  of  concrete,  cement 
plaster,  or  a  double  wall  of  matched  lumber  interlined  with  paper,  and 
with  a  concrete  floor.  Concrete  or  plastered  walls  are  porous  and 
should  be  coated  on  the  inside  with  liquid  asphaltum,  shellac,  or 
silicate  of  soda,  first  painting  once  or  twice  with  a  10  per  cent  solution 


410  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

of  sulfuric  acid  to  prevent  the  liquid  coating  from  peeling  off  after 
drying.  The  door  should  be  of  the  refrigerator  type,  interlined  with 
building  paper  and  closing  with  clamps.  The  interlining  for  wooden 
walls  should  be  a  heavy  glazed  roofing  or  building  paper,  well  lapped 
and  glued  at  the  joints.  Doors  and  windows  should  be  tight  fitting 
and  few  in  number.  For  convenience  in  airing  the  room,  after 
fumigating,  one  window  should  be  made  to  open  from  the  outside. 
If  carbon  disulfid  is  to  be  used,  electric  switches  should  be  placed 
on  the  outside  of  the  room  on  account  of  the  danger  of  explosion. 
Ventilators  provided  for  regulating  the  humidity  should  be  closed 
tightly,  by  covering  with  paper,  while  the  fumigation  is  in  progress. 
Shelving  should  be  of  surfaced  lumber,  free  from  cracks  or  knot  holes, 
and  resting  on  an  angle  iron  frame,  which  facilitates  the  cleaning  of 
both  shelves  and  framework.  Fumigation  should  always  be  done,  if 
possible,  at  a  temperature  of  70°  F.  or  above,  although  good  results 
have  been  secured  at  60°  F.  Insects  are  more  active  at  high  tempera- 
tures and  consequently  take  in  larger  amounts  of  gas ;  for  this  reason 
rooms  held  at  45°  to  60°  F.  should  be  raised  to  a  temperautre  of  65° 
to  70°  F.  for  a  few  hours  just  prior  to  fumigation. 

General  directions  for  fumigation. — Compute  the  capacity  of  the 
room  in  cubic  feet  and  estimate  the  dosage  according  to  the  directions 
for  the  chemical  to  be  used.  During  the  day  prepare  for  fumigation 
by  making  the  room  as  tight  as  possible.  Remove  all  materials,  such 
as  milk,  butter,  and  water,  that  might  absorb  dangerous  quantities  of 
gas  or  become  tainted.  Otherwise  disturb  the  room  as  little  as  possible, 
since  the  less  it  is  disturbed  the  better  the  chance  will  be  of  eradicating 
the  pests.  If  carbon  disulfid  or  sulfur  is  used,  the  additional  pre- 
caution should  be  taken  of  removing  or  coating  with  vaseline  all  nickel 
and  plumbing  or  other  highly  polished  metal  surfaces.  When  the 
preparations  are  complete,  remove  from  the  room  anything  that  might 
be  wanted  during  the  next  twenty-four  hours,  warn  people  in  adjoining 
or  overhead  rooms  of  the  possible  danger,  and  then  set  off  the  charge. 
This  can  usually  be  done  most  conveniently  late  in  the  afternoon,  thus 
giving  an  all-night  exposure  or  preferably  a  twenty-four  hour  exposure, 
if  possible.  It  has  been  found  by  careful  trials,  the  details  of  which 
will  be  given  later,  that  it  is  apparently  unnecessary  to  remove 
para/fined  cheese  from  the  room  during  fumigation.  This  saves  much 
work  in  handling  the  stock  and  prevents  the  possibility  of  infesting 
other  rooms  where  the  cheese  may  be  temporarily  stored.  All  cheese 
remaining  on  the  shelves  should  be  slightly  elevated  on  one  side  to  allow 
free  circulation  of  gas  on  the  underside.     Since  fumigation  has  not 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR   CONTROL 


411 


proved  successful  against  the  skipper  buried  in  the  cheese,  or  possibly 
against  the  egg,  it  becomes  necessary  to  repeat  the  treatment  after 
twelve  to  eighteen  days  in  warm  rooms,  the  shorter  period  being  used 
only  at  maximum  temperatures  above  80°  F.,  while,  as  the  temperature 
drops,  the  time  between  fumigations  lengthens  to  three  weeks  or  more. 
These  dates  are  based  on  the  data  secured  in  breeding  the  fly  under 


Fig.   6. — Surface  of  Jack  cheese   showing  the  pupae  of  cheese  fly  and  the 
cheese  mites  appearing  at  the  points  indicated  by  arrows.     A,  pupa.     B,  mites. 


confinement  and  naturally  are  subject  to  variations.  At  50°  F.  or 
below,  development  is  so  irregular  that  no  definite  time  for  repeating 
the  treatment  can  be  given,  the  first  appearance  of  flies  in  numbers 
being  the  criterion  for  the  next  fumigation. 

Skippers  buried  in  the  cheese  during  the  first  fumigation  would 
probably  escape  alive,  but  may  have  become  susceptible  at  the  second 
fumigation,  either  as  pupae  or  newly  emerged  flies,  and  before  they 


412  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

have  deposited  eggs  for  a  second  generation  of  skippers.  Two  careful 
fumigations  of  the  right  dosage  and  correctly  timed,  followed  by 
thorough  cleaning  should  destroy  all  stages  of  the  pest  as  they  become 
susceptible.  Building  construction  is  so  variable,  however,  that  the 
correct  dosage  is  difficult  to  determine.  An  error  in  the  dosage,  or 
carelessness  in  leaving  a  window  or  a  ventilator  open,  may  render  one 
treatment  valueless.  In  such  cases  a  third  fumigation  is  necessary. 
A  close  watch  should  be  kept  for  flies  several  weeks  after  the  final 
treatment;  if  an  occasional  fly  is  found  it  may  be  killed  with  a  "fly 
swatter"  before  sufficiently  mature  to  oviposit.  If  flies  or  mites  appear 
in  numbers  after  the  second  fumigation,  it  may  be  due  to  one  or  more 
of  four  reasons:  the  fumigation  dosage  was  too  weak;  sanitation  was 
neglected;  flies  entered  from  adjoining  rooms  or  buildings;  or  new 
infestations  were  introduced  in  the  cheese  or  its  containers.  A  study 
of  the  conditions  present  will  probably  show  the  failure  to  be  due  to 
one  or  more  of  these  causes. 

In  all  fumigation  work,  the  difference  between  control  work  and 
eradication  must  be  kept  in  mind.  Control  consists  in  reducing  the 
number  of  the  pests  to  a  point  where  they  will  not  cause  a  serious  loss 
but  where  under  favorable  circumstances  new  outbreaks  may  occur. 
Eradication  means  the  destruction  of  all  stages  of  either  skippers  or 
mites.  The  latter  is  necessarily  moch  more  difficult  to  accomplish 
than  mere  control,  and  where  the  infestation  has  spread  throughout 
the  entire  factory,  it  is  practically  impossible  to  secure  complete 
eradication  unless  the  whole  building  is  fumigated  at  the  same  time. 
This  will  require  special  provision  for  handling  the  milk  outside  the 
factory  during  the  time  required  for  fumigating,  as  it  would  be  very 
dangerous  to  expose  milk  or  water  to  hydrocyanic  acid  gas.  For  snch 
cases  it  is  possible  to  increase  the  charge  and  reduce  the  time  of 
exposure  to  eight  or  ten  hours. 

(I)  Hydrocyanic  acid  gas  has  proved  the  most  efficient  fumigant 
of  any  material  experimented  with,  but  it  is  also  one  of  the  most 
poisonous  chemicals  known.  Even  a  small  particle  of  sodium  or 
potassium  cyanid  may  prove  fatal  if  accidentally  eaten.  It  should 
not  be  handled  without  gloves  if  there  are  cuts  or  abrasions  on  the 
hands.  The  cyanid  for  fumigation  purposes  should  never  he  left  where 
it  may  be  handled  by  those  unacquainted  with  its  deadly  nature,  for 
it  resembles  sugar  and  might  be  eaten  accidentally.  Bo  not  leave  it 
near  food,  milk,  or  water.  Use  it  only  as  directed,  without  any  changes 
in  method  or  of  the  formula,  unless  by  an  experienced  operator. 
Unused  supplies  should  either  be  buried  or  dissolved,  then  greatly 
diluted  and  poured  down  the  sewer.     The  gas  is  vory  dangerous  to 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR  CONTROL 


413 


breathe,  except  in  dilute  quantities,  and  even  the  sulfuric  acid  used  in 
generating  the  gas  burns  severely  if  it  comes  in  contact  with  the  skin. 
One  cannot  too  greatly  emphasize  the  need  of  extreme  care  in  handling 
such  dangerous  chemicals.     If  possible,  the  work  should  be  placed  in 


Fig.  7. — Corner  of  cheese  curing  room  showing  grossly  infested  cheese. 
A,  Colony  of  mites  living  in  a  cracked  cheese  and  on  a  greasy  shelf.  B,  Old 
cheese,  a  possible  breeding  place  for  pests. 


the  hands  of  experienced  operators.  These  warnings,  however,  need 
not  deter  anyone  from  the  use  of  this  valuable  fumigant,  provided 
directions  are  carefully  followed.  Cyanid  has  been  widely  used  as  a 
fumigant  for  orchards,  nursery  stocks,  mills,  warehouses,  and  homes 


414  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION 

for  twenty-five  years,  with  almost  no  fatal  accidents  to  human  beings, 
the  very  few  known  authentic  cases  having  been  due  to  carelessness. 
This  gas  is  not  explosive,  as  is  that  from  carbon  disulfid,  neither  does 
it  have  the  bleaching  or  corroding  effect  of  the  latter  or  of  burning 
sulfur.  These  factors,  coupled  with  its  great  efficiency,  have  increased 
its  popularity  as  a  house  fumigant.  so  that  it  has  largely  displaced 
other  materials,  except  for  quantities  of  stored  products  where  great 
penetration  is  desired. 

Materials  used  in  fumigation. — Potassium  cyanid  was  until  recently 
the  most  common  form  on  the  market.  This  has  been  displaced  by 
sodium  cyanid  which,  for  fumigating  purposes,  is  made  in  one-ounce 
lumps  to  avoid  the  necessity  of  weighing.  It  should  be  98  to  99  per 
cent  pure  and  contain  50  to  51  per  cent  cyanogen.  There  are  grades 
of  cyanid  on  the  market  for  artisans'  and  miners'  use,  which  are  much 
weaker  (50-60  per  cent  pure  instead  of  98  per  cent)  and  these  should 
be  used  in  proportionately  greater  amounts. 

The  gas  is  generated  by  adding  the  cyanid  to  a  solution  of  sulfuric 
acid.  The  commercial  acid  used  in  testing  milk  ahd  cream  is  as  satis- 
factory for  this  purpose  as  the  refined  grade.  The  water  required  in 
the  generation  of  gas  prevents  the  acid  from  charring  the  cyanid. 
generates  heat  by  combining  with  the  acid,  and  holds  in  solution  the 
sodium  sulfate  which  is  formed. 

The  amount  of  sodium  cyanid  required  for  a  tightly  built  room  is 
I1/*  ounces  per  100  cubic  feet,  the  chemicals  being  used  in  the  follow- 
ing proportions : 

Sodium  cyanid iy2  pounds 

Sulfuric  acid 2*4  pints 

Water 3  pints 

A  room,  10x16x10  feet,  contains  1600  cubic  feet  and  would 
require  1  ]A  pounds  of  sodium  cyanid,  2V4  pints  (66  ounces  by  weight) 
of  sulfuric  acid,  and  3  pints  of  water.  The  proportions  for  the  chem- 
icals given  should  not  vary,  but  the  amount  used  per  hundred  cubic 
feci  musl  be  determined  according  to  the  tightness  of  the  room.  The 
above  amount  of  cyanid  may  be  reduced  one-third  in  a  room  built 
especially  for  fumigating  pin-poses,  with  a  corresponding  change  in 
the  amounts  of  acid  and  water.  Twice  the  above  dosage,  or  even  more, 
should  he  used  for  buildings  of  only  approximate  tightness.  Generally 
speaking,  it  is  safer  to  us*1  an  excess  of  cyanid  and  acid  than  to  fall 
below  the  standard  given,  for  i\  weals  concentration  of  gas  will  accom- 
plish nothing. 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR   CONTROL 


415 


Process  of  fumigation. — Earthenware  jars  or  wooden  buckets  make 
good  generators,  tall  narrow  ones  being  preferable  to  low,  broad  ones. 
If  a  wide-botton  generator  is  used,  the  water  and  acid  solution  may  be 
so  shallow  that  the  cyanid  will  not  be  entirely  dissolved.  To  avoid  this 
danger  it  may  be  necessary  to  use  an  excess  of  the  dilute  acid  to  insure 
covering  the  lumps  of  cyanid,  but  the  better  plan  is  to  use  the  normal 
amounts  of  ingredients  in  a  deep,  narrow  container.  Large  rooms 
should  have  two  or  more  generators,  none  of  which  should  contain 


Fig.  8. — Curing  room  constructed  of  tongue  and  groove  lumber,  showing- 
crack  (a)  too  large  to  permit  effective  fumigation. 

more  than  2y2  pounds  of  cyanid,  and  for  this  amount  a  five  or  six- 
gallon  generator  should  be  used.  Since  hydrocyanic  acid  gas  is  lighter 
than  air,  the  generator  is  placed  at  the  lowest  level,  the  floor  and 
everything  within  three  feet  of  the  generator  being  protected  by  a  mat 
of  newspapers  to  avoid  any  possible  spatter  of  acid. 

The  water  is  first  measured  and  poured  into  the  generator,  next  is 
added  the  required  volume  of  acid,  poured  in  slowly  to  avoid  splash- 
ing. Do  not  reverse  the  order  of  mixing,  as  severe  spattering  may 
result.  The  water  and  acid  should  be  combined  immediately  before 
generating  the  gas,  as  an  acid  solution  of  about  180°  F.  will  free  more 
gas  than  a  cold  solution.  The  cyanid,  which  should  be  placed  in  a 
paper  bag  to  delay  the  generation  of  the  gas,  is  now  dropped  into 
the  acid  solution,  and  the  operator  must  then  leave  the  room  as  quickly 


416  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

as  possible,  closing  and  locking  the  door  behind  him.  As  a  further 
precaution,  a  notice  should  be  attached  to  the  outside  of  each  door, 
stating  that  the  room  is  being  fumigated  and  should  not  be  entered. 
Occupants  of  adjoining  rooms  or  those  overhead  should  be  notified  of 
the  operation,  as  sufficient  gas  might  escape  into  these  rooms  to  cause 
serious  danger  to  the  occupants.  The  room  should  be  closed  for  at 
least  twelve  and  preferably  for  twenty-four  hours.  A  door  or  window 
should  then  be  opened  from  the  outside  and  the  room  ventilated  before 
anyone  is  allowed  to  enter. 

(II)  Carbon  disulfid  is  an  oily  liquid  giving  rise  to  a  heavy  vapor, 
which  when  confined  at  a  sufficient  concentration,  is  poisonous  to 
insects  and  higher  animals.  This  material  is  not  so  dangerous  to 
handle  as  hydrocyanic  acid  gas,  but  care  must  nevertheless  be  taken 
by  the  operator  while  working  with  it.  Although  the  gas  has  a  strong 
odor,  it  quickly  deadens  the  sense  of  smell,  so  that  the  operator  may 
not  realize  that  he  is  still  exposed  to  the  fumes;  continued  exposure 
may  be  followed  by  nausea  and  dizziness,  ending  in  suffocation.  On 
account  of  this  danger,  it  is  always  best  for  two  men  to  work  together 
in  fumigating  a  large  building.  Since  the  gas  is  heavier  than  the  air 
and  will  always  settle  to  the  lowest  levels,  it  should  be  exposed  above 
the  highest  layer  of  the  material  to  be  fumigated. 

Process  of  fumigation. — The  amount  of  carbon  disulfid  to  be  used 
varies  from  ten  to  thirty  pounds*  per  1000  cubic  feet,  according  to  the 
tightness  of  the  room  or  bin,  the  larger  amount  being  for  a  room  of 
only  approximate  tightness. 

The  carbon  disulfid  is  poured  into  broad-bottomed,  shallow  pans 
which  may  be  placed  directly  on  top  of  the  material  to  be  treated  or 
on  the  highest  points  in  the  room  which  are  easily  accessible.  The 
pans  should  not  be  filled  more  than  one-half  inch  deep,  as  it  is  necessary 
to  expose  to  the  air  as  large  a  surface  of  the  chemical  as  possible  and 
every  effort  should  be  made  to  hasten  its  vaporization.  The  use  of  a 
spray  pump  is  very  convenient  for  distributing  the  liquid  over  the 
material  to  be  fumigated,  or  against  the  exposed  walls  and  ceilings 
when  large  rooms  are  being  treated.  Another  method  is  to  hang  waste, 
saturated  in  the  carbon  disulfid  at  different  places  in  the  upper  part 
of  the  room.  The  room  is  closed  from  twelve  to  twenty-four  hours  and 
then  well  ventilated  before  anyone  is  allowed  to  enter.  The  same 
precautions  against  accident  should  be  taken  as  with  cyanid. 

(Ill)   Sulfur  has  proved  effective  against  the   cheese  mite,  and 
in  some  instances  would  probably  kill  the  adult  fly,  but  it  cannot 


*  A  pint  of  the  liquid  will  weigh  about  1.3  pounds. 


Bulletin  343] 


CHEESE  PESTS  AND  THEIR  CONTROL 


417 


be  depended  upon  to  kill  the  skipper  or  the  pupal  stages  of  the  cheese 
fly.  Sulfur  fumes  will  corrode  nickel  and  in  the  presence  of  moisture 
will  bleach  colored  fabrics.  The  usual  precautions  of  tightening  rooms 
and  working  at  a  temperature  of  60°  F.  or  above  should  be  taken. 
When  sulfur  candles  are  used,  they  may  be  placed  on  a  float  in  a  tub 
of  water,  lighted,  and  the  room  closed.  Coarse  grades  of  sulfur  may 
be  burned  in  metal  containers.  These  should  be  at  least  twelve  inches 
distant  from  any  inflammable  material.  Time  of  exposure  is  from 
twelve  to  twenty-four  hours. 


Cheese    Curing  Room 

l.ned    with  paper     for    fumijaiioT> 


Fig.  9. — The  cheese  curing  room  shown  in  fig.  8,  with  walls  covered  with 
paper  and  joints  pasted  to  increase  the  effectiveness  of  fumigation. 


FINAL  CONTROL  MEASURES 

After  fumigation  it  is  advisable  to  remove  all  shelving  used  for 
cheese,  scrape  it  thoroughly,  and  wash  with  strong  cleaning  solutions 
or  lye  water  to  remove  the  deposit  of  grease.  Cheese  suspected  of 
being  infested  should  be  disposed  of.  That  which  is  only  slightly 
damaged  may  be  trimmed  and  sold  as  cooking  cheese.  The  trimmings 
and  badly  infested  cheese  should  be  promptly  removed  to  a  distance 
from  the  factory  or  store  room  and  disposed  of  by  burning  or  feed- 
ing to  stock.  Fumigated  rooms  should  be  inspected  every  day  or  two 
for  at  least  one  month  and  preferably  longer  for  the  presence  of 


418 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


the  cheese  fly  in  any  stage,  or  mites.  Adult  flies  may  gain  entrance  to 
the  curing  room  from  other  parts  of  the  building,  but  by  prompt  action 
these  may  be  killed  before  they  have  opportunity  of  ovipositing.  If 
the  control  measures  extend  into  the  fall  months,  or  if  the  rooms  are 
held  permanently  at  65°  F.  or  below,  there  will  be  a  slow  irregular 
development  of  the  pests;  hence  it  becomes  necessary  to  remove  all 
cheese  that  was  exposed  to  infestation,  before  any  skippers  which  may 
be  present  mature.  The  inspection  of  the  uncooled  curing  rooms,  for 
the  presence  of  pests,  should  begin  in  April  and  be  repeated  two  or 
three  times  a  week  during  the  late  spring  and  early  summer.  Neglect 
at  this  time  may  necessitate  the  repetition  of  the  entire  fumigation 
program. 

EXPERIMENTAL  FUMIGATION  DATA 

The  results  secured  in  experimental  work,  leading  up  to  the  deter- 
mination of  effective  dosages,  are  given  in  table  1.  These  data  are 
given  to  emphasize  the  variation  in  results  in  different  types  of 
fumigators  with  varying  lengths  of  exposures. 


TABLE  1 
Fumigating  Experiments*  for  Control  of  Cheese  Skippers  and  Mites t 


Type  of  fumigator 

Cheese  room 
partly  papered 


Fumigant 
used 

Sodium 
cyanid 


Amount 
per  1000 
cu.  ft. 


Length  of 
exposure 


Remarks 


Fumigating  box,        Carbon 
tongue  and  disulfid 

groove  lumber 

Cheese  storage  Sodium 

room,  tight  walls       cyanid 

Five-gallon  stone      Carbon 
jar  disulfid 

Wooden  fumigating  Carbon 
box  disulfid 


Stone  jar 
Stone  jar 


Carbon 
disulfid 


30  ounces    24  hours      Cheese  fly,  exposed  skippers, 

ham    beetles,    and    cheese 
mites  all  killed. 

33  pounds  48  hours      60%  of  skippers  on  surface  of 

cheese  killed,  90%  of  those 
in  cheese  recovered. 

20  ounces    48  hours  All  cheese  mites  killed. 

5  pounds     7.5  hours  All  skippers  alive. 

10  pounds  24  hours  All  skippers  alive. 

10  pounds  24  hours  All  skippers  alive. 


Carbon        20  pounds  24  hours      All  exposed  skippers  dead.  3% 
disulfid  of  those  buried  in  the  cheese 

escaped. 

Wooden  fumigating  Carbon        20  pounds  24  hours      All  skippers  alive, 
box  disulfid 

Stone  jar  Sulfur  10  pounds  26  hours      All  mites  dead.  Skippers  alive. 

(burned) 

*  Temperatures  70°  to  80°  F. 

j  Species  experimented  upon  Tyroglypfms  siro  Gerv. 


Bulletin  343]  CHEESE  PESTS  AND  THEIR  CONTROL  419 

From  the  above  data  it  would  appear  that  the  cheese  fly  larva 
(when  exposed),  the  ham  beetle,  and  the  cheese  mite  may  be  killed  with 
a  dosage  of  from  20  to  30  ounces  of  sodium  cyanid  per  1000  cubic  feet 
in  rooms  approximately  tight.  Skippers  buried  in  the  cheese  cannot 
all  be  killed  even  with  excessive  dosages  of  carbon  disultid  (which  is 
even  a  more  penetrating  gas  than  that  from  sodium  cyanid).  Sulfur 
gave  satisfactory  results  against  the  cheese  mite  in  the  one  experiment 
performed,  but  was  of  no  value  against  the  skipper.  There  has  been 
a  lack  of  opportunity  to  determine  exact  dosages  for  sulfur  in  different 
types  of  fumi gators,  but  the  range  would  probably  be  from  six  to  ten 
pounds  per  1000  cubic  feet  to  control  the  cheese  mite.  This  material 
seems  impracticable  as  a  control  for  the  cheese  fly  except  perhaps  in 
the  adult  stage. 

POSSIBILITY     OF     THE     ABSORPTION     OF     FUMIGATING     GASES     BY     CHEESE 

Practical  fumigation  trials  in  cheese  factories  and  storage  rooms 
have  shown  the  desirability  of  leaving  the  entire  stock  of  chcsc 
untouched  while  the  room  is  being  fumigated.  This  prevents  the 
possibility  of  scattering  the  infestation  and  also  obviates  the  labor  of 
moving  the  stock  in  and  out  of  the  room.  To  determine  whether 
sufficient  amounts  of  the  fumigating  gases  are  absorbed  to  make  it 
dangerous  to  eat  the  cheese  treated,  the  following  experiments  were 
tried  : 

A  test  for  the  absorption  of  gas  was  made  during  the  actual  fumi- 
gation of  a  curing  room,  a  dosage  of  approximately  three  ounces  of 
sodium  cyanid  per  thousand  cubic  feet  being  used.  Time  of  exoosure. 
twenty- four  hours;  temperature  between  60°  and  70°  P.  Twenty 
cheese  fly  pupae  were  placed  in  the  room  prior  to  fumigation  to  test 
the  action  of  hydrocyanic  acid  gas  en  the  fly  in  this  stage.  Five  more 
pupae  of  the  same  age  were  kept  as  a  check.  Flies  emerged  from  each 
of  the  latter  a  Few  days  later,  but  none  from  the  fumigated  pupae. 
The  adult  cheese  fly  and  cheese  mites  were  both  killed  during  this 
treatment.  Four  whole,  paraffined  cheeses  (two  " full-cream '  and 
two  "jack")  and  a  slice  of  freshly  cut  cheese  were  left  in  the  room 
during  fumigation.  These  were  tested  for  odor  or  flavor  of  gas  fifteen 
hours  after  the  opening  of  the  room.  Cuts  were  made  from  the  surface 
and  from  the  inner  portion  of  each  whole  cheese  and  also  from  the 
cut  cheese ;  every  sample  was  tested  by  five  members  of  the  Dairy 
Industry  Division  of  the  University  of  California,  all  of  whom  are 
accustomed  to  competitive  judging  of  commercial  cheese.  In  all. 
twenty-five  people  tried  these  samples,  and  not  one  could  distinguish. 


420  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 

by  taste  or  smell,  the  samples  of  fumigated  cheese  from  those  which 
were  untreated.  Several  ate  freely  of  the  fumigated  cheese  without 
noting  any  ill  effects. 

Effect  of  fumigated  cheese  on  mice* — Two  series  of  experiments 
were  made :  (1)  The  comparative  absorption  of  hydrocyanic  acid  gas 
by  three  unparaffined  "Cheddar"  cheese,  one  of  which  was  a  "skim,' 
another  a  "one-half  skim,"  and  the  third  a  "full  cream"  cheese. 
(2)  The  comparative  absorption  of  the  fumigating  gases  by  aged  and 
fresh  "one-half  skim  milk"  and  "full  cream"  cheese. 

No.  1.    Type  of  cheese  used: 

2  "Cheddar"  "skim  milk"  cheese  made  Sept.  11,  1920. 

1  "Cheddar"  "one-half  skim  milk"  cheese  made  Sept.  9,  1920. 

3  ' '  Cheddar  "  "  full  cream ' '  cheese  made  Sept.  1 2,  1920. 

Date  of  experiment,  Sept.  20,  1920. 

The  experiments  were  conducted  in  special  fumigating  boxes,  one 
being  a  paper-lined,  double-walled  box  of  150  cubic  feet  capacity;  the 
second  of  the  same  size  but  with  concrete  walls,  painted  on  the  inside 
with  liquid  asphalt. 

Time  of  treatment,  24  hours.  Dosage :  Box  1,  ten  ounces  of  sodium 
cyanid  (98  per  cent  pure)  per  1000  cubic  feet;  Box  2,  six  pounds  of 
carbon  disulfid  per  1000  cubic  feet.  Temperature  of  boxes  during 
fumigation,  62°-64°  F. 

To  make  sure  that  a  fatal  dosage  had  been  used,  specimens  of  the 
cheese  mite,  an  adult  cheese  fly,  and  three  pupae  (and  in  Box  1,  a  single 
specimen  of  the  cheese  beetle)  were  placed  in  each  box  during  the 
fumigation  period.  All  these  were  killed  by  the  above  dosage  except 
the  fly  pupae.  The  failure  in  the  case  of  the  latter  can  probably  be 
attributed  to  the  low  temperature  at  which  the  experiment  was  con- 
ducted. After  the  cheese  had  been  fumigated  it  was  removed  and  the 
following  experiments  conducted  with  white  mice:  Series  (A)  and  (B) 
are  alike  except  in  the  fumigating  materials  used,  sodium  cyanid  being 
used  in  the  former  and  carbon  disulfid  in  the  latter. 


*  No  experiments  were  marie  to  determine  the  fatal  dosage  of  hydrocyanic 
acid  gas  to  white  mice,  but  a  number  of  the  common  house  mice  (Mux  musculus) 
were  killed  with  the  ordinary  dosage  while  fumigating  the  storage  room.  Tn 
similar  experiments  made  by  the  United  States  Public  Health  Service9  it  was 
found  that  white  mice  are  quite  susceptible  to  this  gas. 


Bulletin  343]  CHEESE  PEStS  AND  THEIR  CONTROL  421 

Series  A.    Hydrocyanic  acid  gas. 

1.  Two  mice  were  placed  in  a  screened  enclosure  with  fumigated 
cheese,  and  forced  to  eat  from  the  cut  surface  that  had  been  exposed 
to  the  gas. 

2.  The  same  as  experiment  1  except  that  the  cheese  was  aerated  two 
hours  before  the  mice  fed  upon  it. 

3.  Two  mice  were  placed  in  a  screened  enclosure  with  cheese  treated 
as  in  experiment  1.  but  surrounded  with  a  screen  to  prevent  their 
eating  it,  and  were  fed  only  on  unfumigated  cheese. 

4.  Two  mice  were  placed  under  a  bell  jar  with  fumigated  cheese, 
protected  with  a  screen  to  prevent  their  eating  it,  to  determine  if 
enough  gas  was  present  to  kill  by  inhalation. 

5.  Two  mice  were  placed  under  a  bell  jar  with  exposed  cheese, 
aerated  for  two  hours  and  protected  with  a  screen  to  prevent  their 
eating  it,  to  determine  if  danger  from  inhalation  of  gas  had  been 
passed. 

# 

Series  B.  Entire  series  repeated  with  carbon  disulfid  as  the 
fumigant. 

Observations. — The  mice  in  experiments  1  and  2  of  both  series  A 
and  B  suffered  no  ill  effects  from  eating  the  freshly  fumigated  cheese ; 
within  thirty  minutes  after  their  forced  feeding  they  were  eating  freely 
of  the  treated  cheese  upon  which  they  continued  to  feed  for  almost  two 
days.  No  abnormal  conditions  could  be  noted  for  thirty-six  hours 
among  any  of  the  mice  experimented  upon,  during  which  time  they 
were  observed  frequently.  One  mouse  in  series  A,  experiment  1,  died 
forty-two  hours  after  the  forced  feeding.  This  could  have  no  direct 
connection  with  hydrocyanic  acid  gas,  for  death  from  such  a  cause 
would  have  come  very  quickly.  Autopsy  findings  indicated  that  death 
was  caused  by  pneumonia. 

No  difference  could  be  determined  in  the  absorption  of  gas  by  the 
types  of  cheese  used,  from  the  action  of  mice  to  which  it  was  fed. 
Neither  could  more  than  a  mere  trace  of  either  carbon  disulphid  or 
hydrocyanic  acid  gas  be  detected  by  the  operators. 

No.  2.  The  second  series  of  experiments  was  made  to  determine 
the  comparative  absorption  of  fumigating  gases  by  aged  and  fresh 
cheese  and  also  ' '  Cheddar, "  "  one-half  skim ' '  cheese,  and  ' '  full  cream ' ' 
cheese.  The  fumigation  was  begun  on  September  22  and  the  tests  on 
the  mice  were  made  the  following  day.  The  work  was  conducted  in 
the  same  fumigating  box,  with  the  details  of  dosage,  length  of  exposure, 


422  UNIVERSITY  OF   CALIFORNIA— EXPERIMENT  STATION 

and  temperature  similar  to  those  of  series  1,  except  that  this  experi- 
ment was  with  hydrocyanic  acid  gas  alone.  The  same  tests  were  used 
on  the  mice  as  in  the  first  series. 

Types  of  cheese  used : 

2  "Cheddar  skim  milk"  cheese  made  June  29,  1921. 
1  "Cheddar  full  cream"  cheese  made  June  9,  1920. 
1  "Cheddar  full  cream"  cheese  made  April  17,  1920. 
1  "Cheddar  one-half  skim  milk"  cheese  made  June  29,  1920. 
Date  of  experiment,  Sept.  22,  1920. 

Observations. — Cheese,  thirty  minutes  after  removal  from  the  fumi- 
gator,  had  a  slightly  perceptible  odor  which  one  person  identified  as 
hydrocyanic  acid  gas.  At  this  time  both  persons  making  the  test  ate 
cheese  the  size  of  a  walnut  and  smaller  pieces  with  no  ill  effects 
whatever. 

The  mice  in  experiment  2  attempted  to  feed  on  freshly  fumigated 
cheese  within  five  minutes  after  being  placed  in  the  cage.  Apparent 
distaste  was  shown  at  this  time,  but  within  fifteen  minutes  both  mice 
were  feeding  freely  from  this  same  cheese. 

No  ill  symptoms  were  noted  among  any  of  the  mice  experimented 
upon  five  hours  after  they  had  eaten  the  freshly  fumigated  cheese.  A 
few  of  the  mice  escaped  that  night  and,  owing  to  unavoidable  circum- 
stances, mice  died  the  following  day  both  in  the  check  and  among  those 
experimented  on.  No  fatalities  or  abnormal  conditions  occurred  which 
could  be  attributed  to  the  action  of  the  hydrocyanic  acid  gas. 

Many  samples  of  cheese  fumigated  at  different  times  were  examined 
by  several  persons,  including  cheesemakers  and  expert  judges  of  dairy 
products,  and  in  no  instance  did  they  detect  any  odor  or  flavor  of  the 
fumigating  gases.  However,  two  people,  accustomed  to  working  with 
hydrocyanic  acid  gas,  detected  it  in  fumigated  cheese  in  another  series 
of  experiments.  This  odor  was  entirely  lost  after  a  short  aeration. 
Three  persons  ate  one-half  ounce  or  more  of  the  freshly  fumigated 
cheese  without  ill  effects. 


BULLETIN  343]  CHEESE  PESTS  AND  THEIR  CONTROL  423 


SUMMARY 

Cheese  skippers  and  mites  attack  cheese  in  almost  every  part  of  the 
world.  They  are  widely  distributed  in  the  United  States  and  are 
frequently  reported  from  the  principal  cheese-producing  states. 

The  loss  caused  by  these  pests  arises  from :  cheese  actually  eaten, 
damaged  appearance  of  attacked  stocks,  prejudiced  customers,  annoy- 
ance to  manufacturers  and  dealers,  and  the  expense  of  control  measures. 

Old  cheese  with  broken  paraffin  covering,  greasy  shelves,  dirty 
factories,  and  warm  curing  rooms  favor  the  development  of  skippers 
and  mites. 

Fresh  cheese  is  seldom  attacked  by  either  pest,  but  infestation  may 
begin  during  or  at  any  time  after  the  first  month  of  the  curing  period. 

Cold  storage  of  cheese  at  30°  to  36°  F.  is  the  most  practical  method 
of  preventing  loss  from  either  skippers  or  mites.  If  cold  storage  is 
unavailable  the  cheese  should  be  marketed  while  fresh. 

Paraffining  cheese  aids  in  protecting  it  from  attack  if  the  coating  is 
unbroken. 

Fumigation  of  infested  rooms  with  hydrocyanic  acid  gas  or  carbon 
disnlphid  is  the  most  efficient  method  known  for  controlling  both 
skippers  and  mites. 

Hydrocyanic  acid  and  carbon  disulphid  are  dangerous  poisons  and 
should  be  used  only  as  directed,  and  if  possible,  only  by  experienced 
operators.  Do  not  leave  them  where  they  may  be  handled  by  those 
unacquainted  with  their  dangerous  nature. 

Fumigation  should  always  be  supplemented  by  a  thorough  cleaning 
of  the  infested  rooms  and  the  prompt  disposal  of  all  aged  cheese. 

It  is  apparently  unnecessary  to  remove  cheese  from  a  room  during 
fumigation;  the  risk  of  scattering  the  infestation  while  transporting 
the  stock  to  another  room  and  the  expense  of  handling  may  thns  be 
avoided. 

Cheese  of  different  types  and  ages  showed  no  absorption  of  hydro- 
cyanic acid  gas  or  carbon  disulphid.  The  odor  which  was  apparent 
immediately  after  removal  from  the  fumigating  room  disappeared 
after  a  short  aeration.  The  cheese  had  no  objectionable  odor  or  flavor 
when  eaten  two  hours  later. 

Sulfur  burned  in  the  fumigating  room  gave  a  partial  control  of  the 
mites  but  was  of  little  value  against  the  skipper. 


424  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


LITERATURE  CITED 

i  Banks,  Nathan. 

1906.     A  revision  of  the  Tyroglphidae  of  the  United  States.     U.  S.  Dept.  of 
Agr.  Bur.  Ent.,  Tech.  Ser.,  no.  13,  pp.  34. 

2  Eales,  Nellie  B. 

1917a.  The  life  history  and  economy  of  the  cheese  mite.    Annals  Appl.  Biol., 

vol.  4,  pp.  28-35. 
1917b.  Cheese  mites.    Jour.  Bd.  Agr.  (London),  vol.  24,  no.  10,  pp.  1087-1096. 

3  Howard,  L.  O.,  and  Marlatt,  C.  L. 

1896.     The  principal  household  insects  of  the  United  States.     U.  S.  Dept. 
Agr.  Div.  Ent.,  Bull.  4,  pp.  1-130. 

4  HOYT,  C.  F.,  AND  ASSELTINE,  H.   G. 

1921.     California  dairy  products.    Calif.  State  Dept.  Agr.,  Cir.  3,  pp.  11. 

s  Michael,  A.  D. 

1901a.  British  Tyroglyphidae  (London,  Adlard  and  Son),  vol.  1,  pp.  1-291, 
pis.  a-c,  1-19  (see  pp.  135-136). 

1901&.  Op.  cit.,  p.  150. 

«  Mote,  Don  C. 

1914.     The  cheese  skipper.     Ohio  Naturalist,  vol.  14,  no.  7,  pp.  309-316. 

7  Murfeldt,  Mary  E. 

1893.     The  cheese  or  meat  skipper.    U.  S.  Dept.  Agr.  Div.  Ent.,  Insect  Life, 
vol  6,  no.  2,  pp.  170-176. 

s  Tyron,  H. 

1903.     The  cheese  mite.     Queensland  Agr.  Jour.,  vol.  13,  no.  1,  pp.  56-58. 
»  United  States  Public  Health  Reports,  vol.  35,  no.  27,  pp.  1597  (July  2,  1920). 
Jo  Annual  production  report  of  manufactured  dairy  products  and  oleomargarine, 

1920.    U.  S.  Dept.  Agr.  Bureau  of  Markets  Report. 

n  Whitmarsh,  R.  D. 

1912.     Insect  pests  of  the  household.     Ohio  Univ.   Exper.   Sta.   Bull.   253. 
pp.  1-152  (see  p.  148). 


STATION  PUBLICATIONS  AVAILABLE  FOR  FEEE  DISTRIBUTION 

BULLETINS 


No. 
241. 
246. 
251. 


253. 

261. 

262. 

263. 
267. 
268. 
270. 


273. 

275. 

276. 
278. 
279. 
280. 

282. 

283. 

285. 
286. 
287. 
294. 
297. 
298. 
299. 
304. 

308. 


No. 

"Vine  Pruning  in  California,  Part  I.  309. 

Vine  Pruning  in  California,  Part  II. 

Utilization  of  the  Nitrogen  and  Organic  310. 

Matter   in    Septic    and   Imhoff   Tank  312. 

Sludges.  313. 

Irrigation   and   Soil   Conditions  in  the  316. 

Sierra  Nevada  Foothills,  California.  317. 

Melaxuma    of    the    Walnut,     "Juglans 

regia."  320. 

Citrus   Diseases  of  Florida   and   Cuba  321. 

Compared  with  Those  of  California.  323. 

Size  Grades  for  Ripe  Olives. 

Experiments  with  Stocks  for  Citrus.  324. 

Growing  and  Grafting  Olive  Seedlings. 
A  Comparison  of  Annual  Cropping,  Bi-  325. 

ennial  Cropping,  and  Green  Manures 

on  the  Yield  of  Wheat. 
Preliminary  Report  on  Kearney  Tine-  330. 

yard  Experimental  Drain.  331. 

The  Cultivation  of  Belladonna  in  Cali-  332. 

fornia.  334. 

The  Pomegranate. 

Grain  Sorghums.  335. 

Irrigation  of  Rice  in  California. 
Irrigation  of  Alfalfa  in  the  Sacramento  336. 

Valley. 
Trials  with  California  Silage  Crops  for  337. 

Dairy  Cows.  339. 

The  Olive  Insects  of  California. 
The  Milk  Goat  in  California.  340. 

Commercial  Fertilizers. 

Vinegar  from  Waste  Fruits.  341. 

Bean  Culture  in  California.  342. 

The  Almond  in  California.  343. 

Seedless  Raisin  Grapes.  344. 

The  Use  of  Lumber  on  California  Farms. 
A  Study  on  the  Effects  of  Freezes  on  34  7. 

Citrus  in  California. 
I.  Fumigation  with  Liquid  Hydrocyanic 

Acid.  II.  Physical  and  Chemical  Prop- 
erties of  Liquid  Hydrocyanic  Acid. 


I.  The  Carob  in  California.  II.  Nutri- 
tive Value  of  the  Carob  Bean. 

Plum  Pollination. 

Mariout  Barley. 

Pruning  Young  Deciduous  Fruit  Trees. 

The  Kaki  or  Oriental  Persimmon. 

Selections  of  Stocks  in  Citrus  Propa- 
gation. 

Control  of  the  Coyote  in  California. 

Commercial  Production  of  Grape  Syrup. 

Heavy  vs.  Light  Grain  Feeding  for 
Dairy  Cows. 

Storage  of  Perishable  Fruit  at  Freezing 
Temperatures. 

Rice  Irrigation  Measurements  and  Ex- 
periments in  Sacramento  Valley, 
1914-1919. 

Dehydration  of  Fruits. 

Phylloxera-Resistant  Stocks. 

Walnut  Culture  in  California. 

Preliminary  Volume  Tables  for  Second- 
Growth  Redwoods. 

Cocoanut  Meal  as  a  Feed  for  Dairy 
Cows  and  Other  Livestock. 

The  Preparation  of  Nicotine  Dust  as 
an  Insecticide. 

Some  Factors  of  Dehydrater  Efficiency. 

The  Relative  Cost  of  Making  Logs  from 
Small  and  Large  Timber. 

Control  of  the  Pocket  Gopher  in  Cali- 
fornia. 

Studies  on  Irrigation  of  Citrus  Groves. 

Hog  Feeding  Experiments. 

Ohopse  Pests  and  Their  Control. 

Cold  Stornsre  as  an  Aid  to  the  Market- 
ing of  Plums. 

The  Control  of  Red  Spiders  in  Decidu- 
ous Orchards. 


CIRCULARS 


No.  No. 

70.   Observations    on    the    Status    of    Corn  172. 

Growing  in  California.  173. 

82.   The  Common  Ground  Squirrels  of  Cali- 
fornia. 174. 

87.   Alfalfa.  175. 

110.  Green  Manuring  in  California. 

111.  The  Use  of  Lime  and  Gypsum  on  Cali-  178. 

fornia  Soils.  179. 
113.   Correspondence  Courses  in  Agriculture. 

"115.    Grafting  Vinifera  Vineyards.  181. 

126.  Spravins:  for  the  Grape  Leaf  Hopper. 

127.  House  Fumigation.  182. 
1°9.   The  Control  of  Citrus  Insects. 

138.   The  Silo  in  California  Agricnltnre.  183. 

144.   Oidium  or  Powdery  Mild«w  of  the  Vine.  184. 

148.    "Lungworms."  188. 

151.  Feeding:  and  Management  of  Hocrs.  189. 

152.  Some  Observations  on  the  Bulk  Hand-  190. 

ling  of  Grain  in  California.  193. 

l.r)5.   Bovine  Tuberculosis.  198. 

157.   Control  of  the  Pear  Scab.  201. 

159.    Agriculture  in  the  Imperial  Valley.  202. 
161.   Potatoes  in  California. 

164.  Small  Fruit  Culture  in  California.  203. 

165.  Fundamentals    of    Sugar   Beet   Culture  205. 

under  California  Conditions.  206. 

Ifi6.   The  County  Farm  Bureau.  208. 
167.   Feeding  Stuffs  of  Minor  Importance. 

169.  The  1918  Grain  Crop.  209. 

170.  Fertilizing  California  Soils  for  the  1918  210. 

Crop.  212. 


Wheat  Culture. 

The    Construction    of    the    Wood-Hoop 

Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution   of  Milk. 
The  Packing  of  Apples  in  California. 
Factors    of    Importance    in    Producing 

Milk  of  Low  Bacterial  Count. 
Control     of     the     California     Ground 

Squirrel. 
Extending  the  Area  of  Irrigated  Wheat 

in  California  for  1918. 
Infectious  Abortion   in   Cows. 
A  Flock  of  Sheep  on  the  Farm. 
Lambing  Sheds. 
Winter  Forage  Crops. 
Agriculture  Clubs  in  California. 
A  Study  of  Farm  Labor  in  California. 
Syrup  from  Sweet  Sorghum. 
Helpful  Hints  to  Hog  Raisers. 
County   Organizations   for   Rural   Fire 

Control. 
Peat  as  a  Manure  Substitute. 
Blackleg. 
-Tack  Cheese. 
Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
The  Function  of  the  Farm  Bureau. 
Suggestions  to  the  Settler  in  California. 
Salvaging  Rain-Damaged  Prunes. 


CIRCULARS — Continued 


214. 

215. 
217. 

218. 

219. 
223. 
224. 


225. 
227. 
228. 
230. 

231. 
232. 

233. 
234. 

235. 


Seed  Treatment  for  the  Prevention  of 
Cereal  Smuts. 

Feeding  Dairy  Cows  in  California. 

Methods  for  Marketing  Vegetables  in 
California. 

Advanced  Registry  Testing  of  Dairy 
Cows. 

The  Present  Status  of  Alkali. 

The  Pear  Thrips. 

Control  of  the  Brown  Apricot  Scale 
and  the  Italian  Pear  Scale  on  Decid- 
uous Fruit  Trees. 

Propagation  of  Vines. 

Plant  Diseases  and  Pest  Control. 

Vineyard  Irrigation  in  Arid  Climates. 

Testing  Milk,  Cream,  and  Skim  Milk 
for  Butterfat. 

The  Home  Vineyard. 

Harvesting  and  Handling  California 
Cherries  for  Eastern  Shipment. 

Artificial  Incubation. 

Winter  Injury  to  Young  Walnut  Trees 
during  1921-22. 

Soil  Analysis  and  Soil  and  Plant  Inter- 
relations. 


236.  The  Common  Hawks  and  Owls  of  Cali- 

fornia  from   the    Standpoint   of   the 
Rancher. 

237.  Directions  for  the  Tanning  and  Dress- 

ing of  Furs. 

238.  The  Apricot  in  California. 

239.  Harvesting  and  Handling  Apricots  and 

Plums  for  Eastern  Shipment. 

240.  Harvesting    and    Handling    Pears    for 

Eastern   Shipment. 

241.  Harvesting  and  Handling  Peaches  for 

Eastern   Shipment. 

242.  Poultry  Feeding. 

243.  Marmalade  Juice  and  Jelly  Juice  from 

Citrus  Fruits. 

244.  Central  Wire  Bracing  for  Fruit  Trees. 

245.  Vine  Pruning  Systems. 

246.  Desirable  Qualities  of  California  Bar- 

ley for  Export. 

247.  Colonization  and  Rural  Development. 

248.  Some  Common  Errors  in  Vine  Pruning 

and  Their  Remedies. 

249.  Replacing  Missing  Vines. 
252.   Supports  for  Vines. 


